function sharpness,a,xpos,ypos,w,l

dxa=deriv(total(a(xpos(0)-l:xpos(0)+l,xpos(1)-w:xpos(1)+w),2)/float(2*w+1))
mx=max(dxa,min=mn) & xsharp=mx-mn

dya=deriv(total(a(ypos(0)-w:ypos(0)+w,ypos(1)-l:ypos(1)+l),1)/float(2*w+1))
mx=max(dya,min=mn) & ysharp=mx-mn

return,[xsharp,ysharp]
end